Combinations of EDTA-Tris and gentamicin, oxytetracycline in normal bovine milk were examined for synergistic activities aganist Staphylococcus aureus, Streptococcus agalactiae, Corynebacterium Pyogenes, Escherichia coli, Salmonella dublin, Pseudomonas aeruginosa, and proteus spp. isolated from the milk of acute clinical bovine mastitis. The results were summarized as follows: 1. The minimal inhibitory concentrations of EDTA-Tris and gentamicin, oxytetracycline on Escherichia coli, Salmonella dublin, proteus spp., Pseudomonas aeruginosa, Staphylococcus aureus, and Streptococcus agalactiae were markedly reduced. 2. The significant synergistic effects observed when the microorganisms were reacted with EDTA-Tris and gentamicin, oxytetracycline. These findings were respectively verified by kinetic studies of microbial death, using one-fourth minimal inhibitory concentrations of EDTA-Tris, gentamicin, and oxytetracycline.